Early detection of specific classes of pathogens is accomplished by the innate immune system with the help of pattern recognition receptors (PRRs). The detected pathogens include viruses, bacteria, protozoa and fungi, and each constitutively expresses a set of class-specific, mutation-resistant molecules called pathogen-associated molecular patterns (PAMPs).
Toll-like receptors (TLRs) are an important family of PRRs and are widely expressed on innate immune cells, including dendritic cells (DCs), macrophages, mast cells, neutrophils, endothelial cells and fibroblasts. TLRs have broad specificity for conserved molecular patterns shared by bacteria, viruses and parasites.
A number of different TLRs have been characterized. These TLRs bind and become activated by different ligands, which in turn are located on different organisms or structures. The development of immunopotentiator compounds that are capable of eliciting responses in specific TLRs is of interest in the art.
For example, reference 1 discloses a broad class of small molecule immunopotentiators (SMIPs) that are TLR7 agonist compounds. Immunogenic compositions and pharmaceutical compositions comprising these compounds are also disclosed in the reference.
It is an object of the invention to provide salt forms of a specific TLR7 compound having formula (I) shown below which have improved properties, such as improved solubility and photo-stability and reducing the gelling nature of the salt when compared to the free base.